When a high power switch (such as a field effect transistor) opens under load, it is common to see a high magnitude, high rate-of-change voltage across the power switch immediately following the opening of the high-power switch. Unfortunately, such a transient condition can cause damage to the power switch, and/or to other peripheral circuits, either nearby, or directly or indirectly connected to the power switch.
The main cause of the switching transient is the potential for some finite, unpredictable amount of inductance, (L), in series with the power circuit being interrupted by opening of the switch. The energy built up in such inductance based on current flowing through it, causes that current to continue to flow through or around the power switch even after it has been opened. Eventually, the flow of energy from the inductive element is dissipated such as via an arc, or in a connected snubbing circuit, or by the main power switch itself, which could potentially cause catastrophic component damage.